Inflammation

沈 弘 德

台北榮總教研部

本章大綱

• Leukocyte migration

• Cell-adhesion molecules

• Mediators of inflammation

• The inflammatory process

• Anti-inflammatory agents

Lymphocyte recirculation routes

* Extravasation

* Cell-adhesion molecules (CAMs) (endothelial cells & leukocytes)

- selectins- mucins- integrins- ICAMS

* Receptors bind to CAMs

General structures of the four families of cell-adhesion molecules

* Interact with sialylated carbohydrate moieties of mucin-like molecules.

* Responsible for the initial stickiness of leukocytes to vascular endothelium.

* Glycosylated proteins * Heterodimeric proteins* Expressed by leukocytes* Facilitate adherence (LAD disease)

* Contain Ig/mucin-like domains* Expressed on endothelial cells* Bind to integrin/selectin molecules

Steps in neutrophil extravasationInflammatory response↓ cytokines, inflammatory mediatorsVascular endothelium activatedIncreased expression of CAMs

The neutrophil tumblesend-over-end alongthe endothelium.

Neutrophil activationby chemoattractantstimulus: chemokines,PAF, C5a, C3a, C5b67,bacterial peptides

Receptor activation-induced conforma-tional change in the integrin molecules →increased affinity &adhesion

The neutrophilmigrates through the vessel wall intothe tissues.

Cell-adhesion molecules and chemokines involved in the first three steps of neutrophil extravasation

rolling activation

adhesion

Schematic cross-sectional diagram of a lymph node postcapillary venule with high endothelium (HEV)

Each of the secondary lymphoid organs, with the exception ofthe spleen, contains HEVs.

As many as 1.4 x 104

lymphocytes extravasateevery second through HEVsinto a single lymph node.

Lymphocytes attached to the surface of a high-endothelial venule

Naïve T cell tend to home to secondary lymphoid tissues through their HEV regions

(Homing receptor)

Activation of a naïve celloccurs within secondarylymphoid tissue.

(Mucin-like CAM)

Steps in extravasation of a naïve T cell through a high endothelial venule into a lymph node

(a homing receptor)

• Lymphocyte-specific chemoattractants

• G-protein-coupled receptors

• Activation of integrin molecules

Mediators of inflammation

• Chemokines and other mediators released by tissue mast cells, blood platelets, leukocytes and lymphocytes.

• Mediator-producing systems in plasma:- the kinin system- the clotting system- the fibrinolytic system - the complement system

• Some lipids act as inflammatory mediators• Some cytokines are important inflammatory mediators

Chemokines

- key mediators of inflammation

Chemokines

• A superfamily of small polypeptides (90-130 aa residues)• Major regulators of leukocyte traffic (adhesion, chemotaxis, activation)• Involved in inflammation, homeostatic/developmental processes, angiogenesis, wound healing• Induced in response to infection → Assembly of leukocytes at sites of infection

• > 50 chemokines, possess 4 conserved cysteine residues (C-C subgroup, C-X-C subgroup)• > 15 chemokine receptors (CC receptors, CXC receptors)• The interaction between chemokines and their receptors is of high affinity (Ka > 109) and high specificity.

Chemokines signal through receptors coupled with heterotrimeric large G proteins

• Changes in shape of leukocytes• Activation of integrins• Generation of oxygen radicals• Release of granular contents and proteases

Patterns of expression of some principal chemokine receptors on different classes of human leukocytes

*Chemokine-receptor profiles mediate leukocyte activity.

*TH1 cells: CCR1, -3, -5 TH2 cells: CCR3, -4

Plasma enzymes act as inflammatory mediators

Tissue damage induces formation of plasma enzyme mediators by the kinin system, the clotting system, and the fibrinolytic system

(a plasma clotting factor)

C5 C5a +C5b

mast cell degranulation& mediators release

fibrinogen

The complement system

• anaphylatoxins (C3a, C4a, C5a) → mast cell degranulation & mediators (histamine…) release → increase vascular permeability induce smooth-muscle contraction

• C3a, C5a and C5b67 → adhesion, extravasation and migration of monocytes and neutrophils

• Influxes of fluid that carry antibody and phagocytic cells to the site of antigen entry.

Lipids act as inflammatory mediators

The breakdown of membrane phospholipids generates important mediators of inflammation, including thromboxane, prostaglandins, leukotrienes, PAF

(macrophages, monocytes,neutrophils and mast cells)

(platelet-activatingfactor)

Cytokines act as inflammatory mediators

• IL-1, IL-6, TNF-, IL-12, and many chemokines exhibit redundant and pleiotropic effects.

• IL-1, IL-6, TNF-:

• IFN-: attracting & activating macrophages

• IL-12: inducing the differentiation of the proinflammatory TH1 subset

IFN-: contributing to chronic inflammation by attracting and activating macrophages.IL-12: induces the differentiation of the proinflammatory TH1 subsets.

The inflammatory process

The inflammatory process

• acute inflammatory response (neutrophils, 1010/day) - localized inflammatory response (redness, swelling, heat, pain) - systemic acute-phase response

• chronic inflammation (antigen persists) (macrophages) - IFN- - TNF- - fibrosis (scar formation) - granuloma formation• chronic inflammatory diseases

The major local manifestations of acute inflammation

vascular dilation (erythema & warmth)

extravasation of plasma fluid and proteins

Leukocyte emigration and accumulation in the site of injury.

A localized acute inflammatory response

• redness & heatvasodilation - an increase in vascular diameteran increase in the volume of blood in the area

& a reduction in the flow of blood

• swellingan increase in vascular permeabilityleakage of fluid from the blood vesselsan accumulation of fluid in the tissue (edema)extravasation of leukocytes

• activation of the kinin, clotting, fibrinolytic and complement (C53a, C4a, C5a) systems

Macrophages:

- arrive about 5-6 hours after an inflammatory response begins

- exhibit increased phagocytosis

- exhibit increased release of mediators, cytokines and lytic enzymes that contribute to the inflammatory response (IL-1, IL-6, TNF-

Overview of the cells and mediators involved in a local acute inflammatory response

(tissue damage)

*Tissue repair: TGF-, proliferation of fibroblasts, deposition of extracellular matrix

The inflammatory process

• acute inflammatory response (neutrophils, 1010 x 10/day) - localized inflammatory response (redness, swelling, heat, pain) - systemic acute-phase response

• chronic inflammation (antigen persists) (macrophages) - IFN- - TNF- - fibrosis (scar formation) - granuloma formation• chronic inflammatory diseases

Overview of the organs and mediators involved in a systemic acute-phase response

(inhibits the growth of pathogens)

The acute-phase response produces molecules that bind pathogens but not host cells.

On vertebrate cells, these mannose residues are covered by other sugar groups, especially by sialic acid while avoiding complement activation on host cell surfaces.

C/EBP is expressed constitutively in liver hepatocytes and promotes transcription of albumin and transthyretin genes

During an inflammatory response

Comparison of the structure and function of C/EBP and NF-IL6

*Both transcription factors are dimeric proteins containing a leucine-zipper domain and a basic DNA-binding domain.

*Both proteins bind to the same nucleotide sequence in the promoter or enhancer of the genes encoding various liver proteins.

Outcome of acute inflammation

The inflammatory process

• acute inflammatory response (neutrophils, 1010 x 10/day) - localized inflammatory response (redness, swelling, heat, pain) - systemic acute-phase response

• chronic inflammation (antigen persists) (macrophages) - IFN- - TNF- - fibrosis (scar formation) - granuloma formation• chronic inflammatory diseases

A prolonged DTH response can lead to formation of a granuloma

Lytic enzymes released fromactivated macrophages in agranuloma can cause extensivetissue damage.

Roles of IFN- and TNF- in

chronic inflammation

Summary of pleiotropic activity of interferon gamma (IFN-)

*Activated macrophages secrete TNF-a. TNF- acts synergistically with IFN- to initiate a chronic inflammatory response.

Biological activities of TNF-

(endotoxin)

*Endotoxin induces macrophages to produce TNF-, which then

acts to destroy the tumor.

Transgenic mouse (top) bearing a TNF-α transgene becomes anorectic and severely wasted

The inflammatory process

• acute inflammatory response (neutrophils, 1010 x 10/day) - localized inflammatory response (redness, swelling, heat, pain) - systemic acute-phase response

• chronic inflammation (antigen persists) (macrophages) - IFN- - TNF- - fibrosis (scar formation) - granuloma formation• chronic inflammatory diseases

*HEV-like regions: sites of lymphocyte extravasation into the inflamed tissue.

*IFN- and TNF- may play a role in the induction of HEV-like regions along the vasculature.

Leukocyte-adhesion deficiency (LAD) in humans and cattle

- A rare autosomal recessive disease - omphalitis (a swelling and reddening around the stalk of the umbilical cord)

- Patients suffer recurrent and often chronic bacterial infections (inability of their leukocytes to undergo adhesion-dependent migration into sites of inflammation)

- An absence of CD18 (an essential component of a number of integrins)

Anti-inflammatory agents

Anti-inflammatory agents

• Antibody therapies reduce leukocyte extravasation - to block the activity of various adhesion molecules (anti-ICAM-1 + anti-LFA-1)

• Corticosteroids are powerful anti-inflammatory drugs - reduction in the numbers and activity of immune-system cells - prevents NF-B activation - reduces the phagocytic and killing ability of macrophages and neutrophils - reduces chemotaxis - reduces expression of class II MHC molecules and IL-1 production by macrophages - reduces the release of lysosomal enzymes

• NSAIDs combat pain and inflammation

Corticosteroids

• lipophilic• can cross the plasma membrane• form receptor-hormone complex in the cytosol• transported to the nucleus• bind to specific regulatory DNA sequences• induce increased transcription of the NF-B inhibitor (I-B) • binding of I-kB to NF-B in the cytosol• prevent the translocation of NF-B into the nucleus• prevent NF-B activation of a number of genes (genes involved in T cell activation and cytokine production)

Inhibition of cyclooxygenase 1 and 2 by NSAIDs

*Cox-2-specific NSAIDs – inhibit inflammation and do not cause damage to the GI tract

Inflammation

• redness• swelling• heat• pain

• immune-system cells• mediators

Sequence of leukocyte events in inflammation (shown here for neutrophils)